Utility Model G 88 06 642.8 U1 discloses a piston rod for a pneumatic spring in which the piston rod seal is disposed between an inner gas-filled space of a cylinder and an annular space filled with a lubricant. The configuration selected for this piston rod seal is such that the seal is readily fabricated and easily installed. The drawback of such shock absorbers, however, is their relatively high lubricant loss.
A comparable configuration of a compressed-gas spring is shown in DE 38 31 502 A1. To minimize permeation of gases through the seal, seal components having different permeation coefficients are used. This, however, does not prevent an excessive loss of oil during operation.